1. Field of the Invention
This invention relates to gas detection and, in particular, to the detection of sulfur containing gases.
2. Art Background
Employee exposure to hydrogen sulfide (H.sub.2 S) is a significant problem in many industrial environments. For example, cable vaults, particularly in southern regions of the United States, are subject to the presence of H.sub.2 S evolved from the decomposition of vegetation. Alternatively, many industrial processes utilize H.sub.2 S with an attendant possibility of employee exposure to this gas. Since H.sub.2 S is extremely poisonous, e.g., approximately equal toxicity with hydrogen cyanide, the efficient and reliable detection of H.sub.2 S is essential. Present methods for detecting H.sub.2 S generally rely on the discoloration of a treated paper product. For example, paper is treated with a compound such as lead acetate. This compound forms black lead sulfide (PbS) when contacted with H.sub.2 S.
These paper based detectors have various disadvantages. Most significantly, the color change induced by H.sub.2 S for most detectors is not stable and fades. (Certain mercury compounds do not fade but are extremely toxic.) Therefore, the use of detectors to indicate longer term low concentration exposure of employees to H.sub.2 S is quite limited.
Because of the fading problem, the quantitative measurement of H.sub.2 S concentration, especially at concentrations below a few parts per million, is particularly inconvenient since immediate measurement is required. Contact to H.sub.2 S and immediate optical measurement exposes the optical instrument both to corrosion from outgassed H.sub.2 S and to H.sub.2 S from the environment. Prevention of this corrosion while maintaining acceptable accuracy from the measurement is generally excessively expensive. Additionally, the lead compounds used in commercial detectors present a health hazard. This hazard is significant since the compounds are not strongly adherent to the paper backings. Thus, careful handling and storage is required.